1. Technical Field of the Invention
Many electrical appliances, such as blenders, mixers, vacuum cleaners, etc. have a limited warranty from the date of purchase, perhaps ninety-days or one year. This is also true for battery-operated tools, such as drills, saws, sanders, etc. However, in some instances, continuous use may cause failure within the warranty period, thus causing the manufacturer to replace the item prematurely.
Rechargeable batteries used in many appliances and tools have a limited number of recharge cycles before they degrade and fail. It would be useful to determine with some inexpensive indicator when the batteries are nearing the end of their rechargeable life.
There are also electrical instruments that should be recalibrated or checked after a certain number of hours of use. Also, it would be desirable to know how much energy has been expended when using large storage batteries. For these and many other applications, it is desirable to have an inexpensive passive device that both senses the cumulative usage and visually displays, in an irreversible manner the expiration time.
2. Description of the Prior Art
U.S. Pat. No. 4,702,564 teaches the use of a printed tapered bow tie-shaped resistive heating element using silver, silver/carbon conductive inks in thermal contact with an irreversible polyacetylinic material in series with a battery to measure the remaining life in a battery. It also teaches that this device may be used to measure when the warranty on some electrical appliances has been exceeded.
However, it was determined that the thin tapered bow tie or wedge-shaped heater design using conductive silver or silver carbon mixes would, over a period of time at elevated temperatures, degrade and fail. The heaters were unstable and used too much energy.
The instability of the bow tie-shaped wedge silver and silver carbon battery tester is disclosed in U.S. Pat. No. 5,128,616. Here the inventor found the thin section “burned out.” U.S. Pat. No. 5,128,616 discloses a nine-volt battery tester using parallel silver conductive Buss bars connecting adjoining squares of printed carbon heater elements in thermal contact with a reversible thermochromic material.
While this configuration places a significant load on the nine-volt battery tester, it is inefficient and wasteful of both materials and energy as the large carbon rectangular heater elements use a significant amount of current and energy.
The prior art shows the battery testers in series with the batteries. Unfortunately, this would result in measuring the ∫12Δτ.
The prior art does not solve the problem of color changes in the time temperature indicating material when at room temperatures. This can give false readings unless the material is relatively insensitive at room temperatures. Drastic changes in ambient temperature may also present a false reading.
The object of the present invention provides a simple expiration indicator that addresses and solves these problems in a novel, inexpensive, reliable, and efficient way.
It is possible to design electrical circuits and displays to address this problem. However, the cost and complexity limits their application.